The present technology relates to using a two-dimensional hole gas, generated in a channel layer by piezoelectric polarization of a buffer layer, as a carrier of the channel layer.
A compound semiconductor-based field effect transistor (FET) having a GaAs-based or other compound semiconductor layer offers high electron mobility, thus providing excellent n-channel frequency characteristics. Among FETs using an n-channel employed for high-frequency bands are HEMT and JPHEMT (refer, for example, to Japanese Patent Laid-Open No. Hei 11-150264). HEMT is an abbreviation for High Electron Mobility Transistor, and JPHEMT an abbreviation for Junction Pseudomorphic High-Electron-Mobility Transistor.
HEMT is an FET using, as a channel, a high-mobility two-dimensional electron gas induced at a semiconductor heterojunction interface. JPHEMT is an FET that provides an electron mobility higher than HEMP by tolerating a certain degree of lattice mismatch. JPHEMT is an FET that offers improved gate forward voltage (turn-on voltage) by using a pn junction as a gate.
Some of such FETs using an n-channel employ, as a carrier, a two-dimensional electron gas produced on the side of an electron travel layer at the heterojunction interface between an electron supply layer and the electron travel layer as a result of piezoelectric polarization and spontaneous polarization between the electron supply layer and electron travel layer (refer, for example, to Japanese Patent Laid-Open No. 2010-074077 and Japanese Patent Laid-Open No. 2010-045343).